fix(offline): poll navigator.onLine to return online (the online event is unreliable)

The auto-offline -> online return still did not fire: the retry hung on the
'online' event, which an installed PWA often does not deliver. Replace it with a
lightweight poll while in auto-offline that reads navigator.onLine (a reliable
live flag, unlike the event) and only hits the network for a reachability check
when the interface is actually up - so flight mode ON costs no radio, and flight
mode OFF is detected within ~4s and returns online. The 'online' event, when it
does fire, just kicks an immediate check. Runs only in auto-offline (deliberate
offline is the player's choice); wired for both the mid-session and cold-start
auto-offline paths.

ui/src/lib/app.svelte.ts

@@ -587,28 +587,42 @@ function promptOfflineChoice(): Promise<boolean> {
  * cold-start dialog) is left as the player's choice. These are passive OS events — no polling, no
  * battery cost. Web-only and skipped in the mock (the e2e drives connectivity directly).
  */
-// tryReturnOnline is fired from the online event while in auto-offline: the interface being back does
-// not mean the gateway is reachable yet (DNS/routing settle for a moment after flight mode), so it
-// re-checks a few times with backoff before returning online, stopping if the player takes over the
-// state meanwhile. This bounded retry is what actually gets the app back online after flight mode off.
-async function tryReturnOnline(): Promise<void> {
-  for (let attempt = 0; attempt < 4; attempt++) {
+// While in auto-offline, poll for the network to return so the app comes back online — robust to the
+// unreliable `online` event (which often does not fire in an installed PWA). Each tick is cheap: it
+// reads navigator.onLine (no radio) and only hits the network (a reachability check) when the
+// interface is actually up, so while flight mode is on it costs nothing. The poll runs ONLY in
+// auto-offline (a deliberate offline is the player's choice) and stops on returning online.
+let recoveryTimer: ReturnType<typeof setTimeout> | null = null;
+export function scheduleRecovery(delayMs: number): void {
+  if (recoveryTimer) {
+    clearTimeout(recoveryTimer);
+    recoveryTimer = null;
+  }
+  if (typeof window === 'undefined' || !offlineMode.active || !offlineMode.auto) return;
+  recoveryTimer = setTimeout(async () => {
+    recoveryTimer = null;
     if (!offlineMode.active || !offlineMode.auto) return;
-    if (await checkReachable(BOOT_REACHABILITY_TIMEOUT_MS)) {
+    const interfaceUp = typeof navigator === 'undefined' || navigator.onLine;
+    if (interfaceUp && (await checkReachable(BOOT_REACHABILITY_TIMEOUT_MS))) {
       if (offlineMode.active && offlineMode.auto) setOfflineMode(false);
       return;
     }
-    await new Promise((r) => setTimeout(r, 600 * (attempt + 1)));
-  }
+    scheduleRecovery(4000);
+  }, delayMs);
 }
 
 export function initNetworkReactivity(): void {
   if (typeof window === 'undefined' || import.meta.env.MODE === 'mock') return;
   window.addEventListener('offline', () => {
-    if (!offlineMode.active) setOfflineMode(true, false); // auto (session) — self-heals below
+    if (!offlineMode.active) {
+      setOfflineMode(true, false); // auto (session)
+      scheduleRecovery(4000); // poll for the network to return
+    }
   });
+  // The online event, when it fires, just kicks an immediate reachability check; the poll above is
+  // the reliable fallback for platforms where it does not fire.
   window.addEventListener('online', () => {
-    if (offlineMode.active && offlineMode.auto) void tryReturnOnline();
+    if (offlineMode.active && offlineMode.auto) scheduleRecovery(0);
   });
 }
 
@@ -905,6 +919,7 @@ export async function bootstrap(): Promise<void> {
         if (goOffline) {
           // A deliberate dialog choice is sticky; an auto (no-interface) offline is session-only.
           setOfflineMode(true, !interfaceOffline);
+          if (interfaceOffline) scheduleRecovery(4000); // auto-offline: poll for the network to return
           app.session = saved;
           app.profile = cachedProfile;
           if (router.route.name === 'login' || router.route.name === 'confirm') navigate('/');